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Soil-transmitted helminth (STH) infections affect an estimated 2 billion people world wide. Children experience the greatest morbidity, limiting their potential in academic and physical endeavors. Our study assessed the prevalence of STH infections in primary school-aged children in a rural village in the Nyanza Province of Kenya. Over two-thirds (68%) of the sampled population tested positive using a direct smear microscopic analysis of single stool samples. Only heavy worm infections would be detected with this technique; thus 68% is a minimum estimate of prevalence. Prior to our study, there were no deworming programs in this village, despite WHO and Kenyan government guidelines supporting regular deworming programs. Our study demonstrates the significant burden of STH infections in a rural Kenyan village and highlights the need for deworming programs in similar venues. We also demonstrate that with basic infrastructure and community involvement, regular deworming can be implemented effectively in remote, rural communities.
A vaccination trial was conducted to evaluate the potential benefit of Haemonchus contortus gut membrane proteins as vaccine antigens under field conditions in Louisiana. The trial was conducted in the summer of 1996 in a flock of ewes grazing pasture naturally infected with H. contortus. Ewes were randomly assigned to three treatment groups (vaccine, adjuvant only, and saline) and fecal egg counts (FEC, measured as eggs per gram of feces), packed cell volumes (PCV), and antibody levels were monitored fortnightly for 12 weeks. It was shown by FEC that there were large individual variations in susceptibility to H. contortus in both vaccinated and non-vaccinated sheep, a finding which could have masked differences between treatments when analyzed by conventional statistical methods. Based on their egg counts before the period when the vaccination could have had an effect, all ewes were categorized as 'susceptible' or 'relatively resistant'. The significance of differences between FEC, PCV and antibody responses of vaccinated and control sheep were tested separately for the 'susceptible' and 'relatively resistant' category. The 'susceptible' vaccinates shed 65% fewer worm eggs during the period when the vaccine could have had an effect, but the difference was only significant on Week 6 post-vaccination. In these experiments, it was difficult to completely exclude the confounding effect of having 'relatively resistant' sheep in the control group. More studies are needed to further evaluate H11 and H-gal-GP antigens under field conditions.
Changes over time in the prevalence and intensity of Schistosoma mansoni infection were measured by serial quantitative stool examinations using the modified Ritchie concentration technique in a 9-year prospective study of an endemic Puerto Rican community with a population of about 1,000 persons. The complete interruption of transmission was achieved by snail control during the 2nd year of the study, in February 1973. Annual stool specimens were obtained from all willing community residents. In addition, from 27 of these residents 10 consecutive stools were collected in each of 3 years: 1973, 1976, 1977. After a chemotherapy campaign with oxamniquine in 1980, only eight of these 27 persons remained untreated. Ten consecutive stools were collected from seven of these untreated individuals in 1981. We calculated the rate of decline (beta) in geometric mean egg count in the cohort of 27 over 5 years and in the subcohort of seven over 9 years. Similarly, beta was calculated from the change in the single annual stool counts in 528 persons providing data for all of the first 6 years of the study. Estimates of the average life-span (-1/beta, in a model assuming constant rate of death) of the adult S. mansoni with 95% confidence intervals are for the cohort of 27, 5.5 years (4.0 to 9.1), for the cohort of seven, 37 years (8.0 to infinity), and and for the cohort of 528, 35 years (16 to infinity).(ABSTRACT TRUNCATED AT 250 WORDS)
Conflicting interpretations regarding the fecundity of schistosomes infecting human beings have arisen and are, in part, due to the inability to directly measure the parameters. The inability to experimentally manipulate human beings necessitates the use of surrogate variables, i.e., number of eggs per gram of feces, as an indicator of worm burden. This study reanalyzes data from quantitative autopsies performed in Egypt by Cheever and colleagues on individuals with active Schistosoma mansoni infections. Exploratory regression analysis of the relationship of female worms recovered to eggs/g of feces and of female worms to eggs retained in host tissues suggests a linear relationship in both cases. Over the observed range of female worms recovered from an individual human being, the estimated worm fecundity, as measured by the number of eggs either in feces or retained in tissues per female worm, is not significantly different from a constant value. Hence, density-dependent fecundity of S. mansoni in the human host, as suggested by others, is not demonstrated in these data.